Manganese-52 positron emission tomography tracer characterization and initial results in phantoms and in vivo

Purpose: Manganese(II) is employed as a contrast agent with magnetic resonance imaging (MRI) for study of neuronal activation in rats and mice. However, at the concentrations required for MRI, Mn may induce pharmacological or toxic effects. Positron emission tomography (PET) imaging of (MnCl2)-Mn-52 at tracer doses has the potential to allow similar Mn studies as manganese-enhanced MRI while providing quantitative results and avoiding toxic effects. In this work, (MnCl2)-Mn-52 is produced and characterized as a PET tracer in phantoms and in rats. Methods: (MnCl2)-Mn-52 was produced by proton irradiation of natural Cr foil and separated by column chromatography. Images were acquired on a Siemens Focus 120 small animal PET scanner. Phantom images were acquired to assess uniformity, resolution, cascade background correction, and count rate linearity. Images of rats were also acquired after systemic and intracerebroventricular (ICV) administration of (MnCl2)-Mn-52 to investigate Mn(II) distribution in vivo. Results: Irradiation yield was 74.6 +/- 8.5 kBq/mu A min Mn-52 at end of bombardment with initial specific activity of at least 3.5 MBq/nmol. Mn-52 PET images show similar uniformity and resolution to F-18. F-18 based detector efficiency normalization is adequate for Mn-52 imaging. Subtraction of a rescaled random events distribution from sinogram data is effective for cascade correction of Mn-52 PET data. After systemic injection, Mn-52 appears in structures throughout the body of rats, including bones, liver, intestines, and the pituitary gland, but does not appear detectably throughout the brain. After ICY injection, Mn-52 remains in the brain and spinal cord. Conclusions: Mn-52 is a promising tracer for small animal PET imaging, yielding image quality comparable to F-18. Potential applications include studies similar to Mn-enhanced neuronal MRI, and in other organ systems including bones, spinal cord, and the digestive tract. (C) 2013 American Association of Physicists in Medicine. [http://dx.doi.org/10.1118/1.4793756]